1. Field of the Invention
The present invention relates to a data transfer method and related apparatus in a host-slave interface. In particular, it provides a data transfer method in which the host uses direct memory access to unpack a stream of data containing multiple data units received from the slave without memory copy.
2. Description of the Related Art
SDIO (Secure Digital Input Output) is an interface that uses the SD (Secure Digital) card form factor for devices other than flash memory cards. Such devices (the slave device in the SDIO interface) may include GPS receivers, Wi-Fi or Bluetooth adapters, modems, Ethernet adapters, barcode readers, IrDA adapters, FM radio tuners, TV tuners, RFID readers, digital cameras, mass storage media such as hard drives, etc. The host devices (the master in the SDIO interface) that support SDIO may be PDAs (personal digital assistants), laptop computers, cell phones (“smart phones”), etc.
In a conventional host-slave system using the SDIO interface, the host device controls data transfer, and the slave device can only move data according to the host's request. The slave device cannot initiate data transfer. In data transfer, there is a time delay between the request sending of the host device and the request receiving of the slave device, and likewise there is a time delay between the response sending of the slave device and the response receiving of the host device. Such a situation is called inter-command delay. Because the slave device must wait for the host to request data, inter-command delay associated with the request command causes delay in data transfer. The inter-command delay may be as much as hundreds of microseconds.